Method and apparatus for determining the geographic location of a device

ABSTRACT

A method and apparatus for determining the location of a device from signals provided by a plurality of satellites. A device receives a first plurality of signals comprising one signal from each of a first plurality of satellites and determines a first location of the device as a function of the first plurality of signals. The device then determines a second location thereof as a function of a second plurality of signals if the first location is not within a predetermined threshold. The second plurality of signals is a first subset of the first plurality of signals.

BACKGROUND

It is important to determine the location of a mobile telephone or othermobile device capable of radio communication especially in an emergencysituation. One method of assessing geolocation of a mobile device isutilizing the mobile device in conjunction with a geolocation system.Exemplary geolocation systems include satellite navigation systems. Forexample, one Global Navigation Satellite System (GNSS) is the NAVSTARGlobal Positioning System (i.e., GPS). GPS is a radio positioning systemproviding subscribers with highly accurate position, velocity, and time(PVT) information.

FIG. 1 is a schematic representation of a constellation 100 of GPSsatellites 101. With reference to FIG. 1, GPS includes a constellationof GPS satellites 101 in non-geosynchronous orbits around the earth. TheGPS satellites 101 travel in six orbital planes 102 with four of the GPSsatellites 101 in each plane. Of course, a multitude of on-orbit sparesatellites may also exist. Each orbital plane has an inclination of 55degrees relative to the equator. In addition, each orbital plane has analtitude of approximately 20,200 km (10,900 miles). The time required totravel the entire orbit is just under 12 hours. Thus, at any givenlocation on the surface of the earth with clear view of the sky, atleast five GPS satellites are visible at any given time.

With GPS, signals from the satellites arrive at a GPS receiver and areutilized to determine the position of the receiver. GPS positiondetermination is made based on the time of arrival (TOA) of varioussatellite signals. Each of the orbiting GPS satellites 101 broadcastsspread spectrum microwave signals encoded with satellite ephemerisinformation and other information that allows a position to becalculated by the receiver. Presently, two types of GPS measurementscorresponding to each correlator channel with a locked GPS satellitesignal are available for GPS receivers. The two carrier signals, L1 andL2, possess frequencies of 1.5754 GHz and 1.2276 GHz, or wavelengths of0.1903 m and 0.2442 m, respectively. The L1 frequency carries thenavigation data as well as the standard positioning code, while the L2frequency carries the P code and is used for precision positioning codefor military applications. The signals are modulated using bi-phaseshift keying techniques. The signals are broadcast at precisely knowntimes and at precisely known intervals and each signal is encoded withits precise transmission time.

GPS receivers measure and analyze signals from the satellites, andestimate the corresponding coordinates of the receiver position, as wellas the instantaneous receiver clock bias. GPS receivers may also measurethe velocity of the receiver. The quality of these estimates dependsupon the number and the geometry of satellites in view, measurementerror and residual biases. Residual biases include satellite ephemerisbias, satellite and receiver clock errors and ionospheric andtropospheric delays. If receiver clocks were perfectly synchronized withthe satellite clocks, only three range measurements would be needed toallow a user to compute a three-dimensional position. This process isknown as multilateration. However, given the expense of providing areceiver clock whose time is exactly synchronized, conventional systemsaccount for the amount by which the receiver clock time differs from thesatellite clock time when computing a user's position. This clock biasis determined by computing a measurement from a fourth satellite using aprocessor in the receiver that correlates the ranges measured from eachsatellite. This process requires four or more satellites from which fouror more measurements can be obtained to estimate four unknowns x, y, z,b. The unknowns are latitude, longitude, altitude and receiver clockoffset. The amount b, by which the processor has added or subtractedtime is the instantaneous bias between the receiver clock and thesatellite clock.

However, the signal received from each of the visible satellites doesnot necessarily result in an accurate position estimation. The qualityof a position estimate largely depends upon two factors: satellitegeometry, particularly, the number of satellites in view and theirspatial distribution relative to the user, and the quality of themeasurements obtained from satellite signals. For example, the largerthe number of satellites in view and the greater the distancestherebetween, the better the geometry of the satellite constellation.Further, the quality of measurements may be affected by errors in thepredicted ephemeris of the satellites, instabilities in the satelliteand receiver clocks, ionospheric and tropospheric propagation delays,multipath, receiver noise and RF interference. With standalone GPSnavigation or geographic location, where a user with a GPS receiverobtains code-phase ranges with respect to a plurality of satellites inview, without consulting with any reference station, the user is verylimited in ways to reduce the errors or noises in the ranges.

One method and apparatus to eliminate erroneous GPS signals is disclosedby copending U.S. application Ser. No. 11/405,404, filed Apr. 18, 2006by the inventors hereof, entitled, “Method and Apparatus for GeolocationDetermination,” the entirety of which is herein incorporated byreference. This invention compares predicted C/A chips with measuredchips and discards satellite signals having significant inconsistencies.However, pruning erroneous GPS signals based on code phase predictionmay not be necessary if no erroneous signals exist, and such a techniquemay require a reasonably accurate cell database.

Accordingly, there is a need for a method and apparatus for geographiclocation determination of a device that would overcome the deficienciesof the prior art. Therefore, an embodiment of the present subject matterprovides a method for determining the location of a device. The methodcomprises the steps of receiving a first plurality of signals comprisingone signal from each of a first plurality of satellites and determininga first location of the device as a function of the first plurality ofsignals. If the first location is not within a predetermined thresholdthen the method comprises the step of determining a second location ofthe device as a function of a second plurality of signals wherein thesecond plurality of signals is a first subset of the first plurality ofsignals. An alternative embodiment may further comprise the step ofdetermining a third location of the device as a function of a thirdplurality of signals if the second location is not within thepredetermined threshold, wherein the third plurality of signals is asecond subset of the first plurality of signals.

In another embodiment of the present subject matter a method is providedfor determining the location of a device receiving signals from each ofa plurality of satellites, the device having determined a first locationfrom the plurality of satellite. The method comprises the steps ofcomparing a quality of the first location of the device with apredetermined threshold and determining a second location of the devicefrom a first subset of the received signals if the quality of the firstlocation is not within the predetermined threshold. Additionalembodiments may further comprise the step of determining a thirdlocation of the device as a function of a second subset of the receivedsignals if the quality of the second location is not within thepredetermined threshold.

In yet another embodiment of the present subject matter a method isprovided for determining the location of a device. The method comprisesthe steps of receiving a plurality of signals from a plurality ofsatellites, generating estimates of a location of the device usingcombinations of the plurality of signals, and selecting an estimate asdefined by a quality of each of the combinations.

An alternative embodiment of the present subject matter provides anapparatus comprising a receiver for receiving a first plurality ofsignals comprising one signal from each of a first plurality ofsatellites and a means for determining a first location of the apparatusas a function of the first plurality of signals. The apparatus mayfurther comprise a means for determining a second location of theapparatus as a function of a second plurality of signals if the firstlocation is not within a predetermined threshold, wherein the secondplurality of signals is a first subset of the first plurality ofsignals. Additional embodiments of an apparatus according to the presentmatter may further comprise a means for determining a third location ofthe apparatus as a function of a third plurality of signals if thesecond location is not within the predetermined threshold, wherein thethird plurality of signals is a second subset of the first plurality ofsignals.

An additional embodiment of the present subject matter provides anapparatus for determining location from signals received from aplurality of Global Navigation Satellite System (“GNSS”) satellites. Theapparatus comprises a receiver for receiving signals from each of aplurality of satellites, a means for determining a first location of thedevice as a function of a quality of the received signals, and a meansfor determining a second location of the device as a function of asubset of said received signals if said quality is not within apredetermined threshold.

In still another embodiment of the present subject matter a method isprovided for calculating the position of a device. The method comprisesthe steps of receiving a first plurality of observations from a firstplurality of satellites and determining a first position of the deviceas defined by a quality of the first plurality of observations. If thequality of the first plurality of observations fails to meet thepredefined threshold then the method comprises the steps of determininga second position of the device as defined by a quality of a secondplurality of observations, the second plurality being a subset of thefirst plurality of observations. If the quality of the second pluralityof observations fails to meet the predefined threshold then additionalpositions of the device are determined utilizing incrementallydecreasing subsets of observations until a predetermined criteria isachieved.

These embodiments and many other objects and advantages thereof will bereadily apparent to one skilled in the art to which the inventionpertains from a perusal of the claims, the appended drawings, and thefollowing detailed description of the embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic representation of a constellation of GPSsatellites.

FIG. 2 is an algorithm according to one embodiment of the presentsubject matter.

FIG. 3 is an algorithm according to another embodiment of the presentsubject matter.

FIG. 4 is a schematic representation for implementing one embodiment ofthe present subject matter.

DETAILED DESCRIPTION

With reference to the figures where like elements have been given likenumerical designations to facilitate an understanding of the presentsubject matter, the various embodiments of a system and method fordetermining the geographic location of a device are herein described.

The disclosure relates to methods and apparatuses for determininggeolocation using satellite signals as well as for pruning erroneoussatellite signals. The satellites may be considered as part of a GlobalNavigation Satellite System (“GNSS”), such as, for example, the U.S.Global Positioning System (“GPS”). While the following descriptionreferences the GPS system, this in no way should be interpreted aslimiting the scope of the claims appended herewith. As is known to thoseof skill in the art, other GNSS systems operate, for the purposes ofthis disclosure, similarly to the GPS system, such as, but not limitedto, the European Satellite project, Galileo; the Russian satellitenavigation system, GLONASS; the Japanese Quasi-Zenith Satellite System(“QZSS”), and the Chinese satellite navigation and positioning systemcalled Beidou. Therefore, references in the disclosure to GPS and/orGNSS, where applicable, as known to those of skill in the art, apply tothe above-listed GNSS systems as well as other GNSS systems not listedabove.

FIG. 2 is an algorithm 200 according to one embodiment of the presentsubject matter. With reference to FIG. 2, in step 201, a device receivessignals from all satellites within view. The device may be a receiversuch as a mobile unit. An exemplary mobile unit may include a cellulardevice, text messaging device, computer, portable computer, vehiclelocating device, vehicle security device, communication device, orwireless transceiver. While step 201 may be implemented at a device suchas a GPS receiver, step 201 may also be implemented at a differentlocation and communicated to the receiver. For example, if the receiveris adapted to receive cellular signals (e.g., the receiver is part of acellular telephone), the receiver may obtain its approximate locationfrom a cell network's Mobile Location Center (MLC). The MLC may identifythe cell in which the mobile is located or the location of the closestbase station. This information may enable the receiver to possess ageneral understanding of its location (i.e., the receiver is in an areaserviceable by the identified cell). It should also be noted that areceiver is only one exemplary means for implementing the embodimentsdisclosed herein and other means such as a transceiver may be equallyused without departing from the principles of the present subjectmatter.

In step 202, a first location of the receiver may be calculated as afunction of the received from all the satellites within view. Thereceiver may identify each satellite and its location information. Thelocation information may be obtained, for example, by collectingbroadcast ephemeris information from one or more visible GPS satellites.The ephemeris information may also be obtained from a source other thanthe satellite itself. For example, the MLC may be configured to trackthe location of each satellite and provide this information to thereceiver upon request.

In step 203, if the first location calculation is within a predeterminedthreshold, then this location is utilized; however, if the firstlocation calculation is not within the predetermined threshold, then nis set to one (1), wherein n denotes an integer number of satellites. Instep 204, if there are four or more satellite measurements remaining,that is: NumberOfSatellites−n≧4, then the algorithm 200 proceeds to step205 and calculates a location for each different combination ofsatellite measurements while leaving out n satellite measurements foreach combination.. In step 206, if none of the locations calculated arewithin the predetermined threshold, then n is incremented by one (1) andthe algorithm 200 proceeds to step 204.

In step 207, if more than one combination of satellite signals is withinthe predetermined threshold, then the location of the receiver having alowest sum of the squared residuals (SSR), i.e., a measure of thequality of a location fix that is a function of the GPS positioncalculation least squares process, is selected. Of course, locationestimates may be selected based upon ephemeris information or otherinformation indicative of the quality of the satellite signals. Further,if the receiver or device is in communication with a cellular network,location estimates may be selected as a function of information providedby the cellular network. Thus, the algorithm 200 may minimize the numberof combinations or iterations of signals to be tested by first leavingout one satellite signal and then leaving out two, three, etc.,satellite signals.

FIG. 3 is an algorithm 300 according to another embodiment of thepresent subject matter. With reference to FIG. 3, in step 302, a firstplurality of signals is received at a device comprising one signal fromeach of a first plurality of satellites. The device may be a receiversuch as a mobile unit, and an exemplary mobile unit may include acellular device, text messaging device, computer, portable computer,vehicle locating device, vehicle security device, communication device,or wireless transceiver. Of course, step 302 may be implemented at a GPSreceiver or a different location and communicated to the receiver. Thus,the receiver may obtain its approximate location from an MLC, and theMLC may identify the cell in which the mobile is located or the locationof the closest base station. It should also be noted that a receiver isonly one exemplary means for implementing the embodiments disclosedherein and other means such as a transceiver may be equally used withoutdeparting from the principles of the present subject matter.

In step 304, a first location of the device may be determined as afunction of the first plurality of signals. The device may identify eachsatellite and its location information. The location information may beobtained, for example, by collecting broadcast ephemeris informationfrom visible GPS satellites. The ephemeris information may also beobtained from a source other than the satellite itself such as an MLCconfigured to track the location of each satellite and provide thisinformation to the mobile receiver upon request.

In step 306, a second location of the device may be determined as afunction of a second plurality of signals if the first location is notwithin a predetermined threshold. The second plurality of signals is afirst subset of the first plurality of signals. In step 308, a thirdlocation of the device may be determined as a function of a thirdplurality of signals if the second location is not within thepredetermined threshold. The third plurality of signals is a secondsubset of the first plurality of signals. Thus, the algorithm 300 mayminimize the number of combinations or iterations of signals to betested by first leaving out one satellite signal and then leaving outtwo satellite signals. For example, if the first location is not withinthe predetermined threshold, then a second location of the device willbe determined utilizing combinations of satellite signals with onesatellite signal excluded. If the second location is not within thepredetermined threshold, then a third location of the device will bedetermined utilizing combinations of satellite signals with twosatellite signals excluded. If more than one combination of satellitesignals is within the predetermined threshold, then the location of thedevice having a lowest SSR may be selected. Of course, locationestimates may be selected based upon ephemeris information or otherinformation indicative of the quality of the satellite signals, andlocation estimates may be selected as a function of information providedby a cellular network if the receiver or device is in communication withthe cellular network. Thus, algorithms according to the present subjectmatter may provide an incremental method of trialing differentcombinations or subsets of satellite signals as input to a positiondetermination or calculation.

Locations of a device may be conducted by a parametric least-squaresalgorithm or other algorithms known in the art. The parametricleast-squares algorithm is generally based upon a series of matrixmanipulations having at least one output typically identified as thevariance factor. In embodiments of the present subject matter, if thevariance factor is not within a predetermined threshold or issignificantly large, then the device's determined location fails. Such afailure may be the result of one or a combination of several problems.For example, a location may fail because the GPS satellite location wascalculated incorrectly, a seed location utilized to calculate thedevice's position was >100 km from a positioning determining entity'slocation, or inaccuracies in the satellite signals or erroneoussatellite signals were received. Various factors may contribute or causesuch inaccuracies or errors such as ephemeris error, satellite clocktiming error, atmospheric effects, receiver noise and multipath.

If a device receives or calculates erroneous signals and pre-processingof the signals is not performed, the yield of a device's positiondetermination may be significantly affected. A high quality GPS yield iscritical to the operation of an SMLC (serving mobile location center),GMLC (gateway mobile location center), SAS (stand alone SMLC) or SUPL(secure user plane location) platforms. For example, Table 1 illustratesthe effect of erroneous input data in a GPS position determination. Inthe following table, the code phase “chips” measurement for a particularsatellite was manually manipulated to illustrate the effect of erroneousGPS signals.

TABLE 1 Result distance from Chip offset ground truth meters 01.7239967161342793 1 174.19052731004507 2 346.70201634947557 3519.208316511694 4 fail 5 fail

Table 1 provides an illustration of the effect of manipulating the chipsfor one satellite for a particular GPS signal. The table further showsthat the location error increases significantly when the chipsmeasurement is altered, and when the chip measurement is four chips fromthe original value, the least squares implementation cannot convergeupon a solution.

Further testing was conducting by corrupting code phase measurements tosimulate erroneous GPS data. The following results provide a yield (andan accuracy in brackets) when “corrupting” a plurality of satellites ina GPS signal from a NovAtel GPS receiver. The GPS signals in thefollowing example were 80657 distinct pseudorange measurements takenfrom the NovAtel GPS receiver over a twenty-four hour period with anaverage cardinality of eight satellites in view during this period. Forthe following examples, erroneous satellite data was produced throughthe addition of a random number between 0 and 1023 to the measured chipskeeping it in the range from 0 to 1023 as shown below in Equation 1.

chips=((random(_______)*1024)+chips/%1024   (1)

For each GPS signal, the “corrupted” satellite(s) were randomly selectedwithin the GPS signal. Further, the following tables identify the yieldas a percentage with the resulting distance from the ground truth forthe position calculations that succeed.

Table 2 provides an analysis of yield when no attempt is made to removeerroneous satellite (“sat”) signals, i.e., no pre-processing, from aposition determination. The results identified in Table 2 illustratethat with more than one erroneous satellite signal, yield dropssignificantly and unacceptably. The results identified in Table 2 may beindicative of situations encountered in a regional or countryenvironment where there exists little signal interference and cells arelikely to be large (up to 40 km).

TABLE 2 0 bad sats 1 bad sat 2 bad sats 3 bad sats 4 bad sats  1 Kminitial offset 100 (4.2) 89.3 (9.7) 60.7 (22.3) 10.3 (261.2) 7.8 (530.9) 5 Km offset 100 (4.2) 89.2 (9.0) 60.8 (18.2) 10.4 (213.3) 7.9 (663.7)10 Km offset 100 (4.2) 89.2 (8.0) 60.7 (20.3) 10.5 (238.4) 7.9 (631.9)15 Km offset 100 (4.2) 89.2 (9.3)  60.5 (22.11) 10.4 (257.9) 7.9 (643.3)20 Km offset 100 (4.2) 89.2 (8.4) 60.7 (28.7) 10.5 (301.2) 7.9 (657.0)25 Km offset 100 (4.2) 89.9 (8.5) 60.6 (20.6) 10.4 (305.9) 8.0 (601.0)30 Km offset 100 (4.2) 89.6 (8.8) 60.7 (28.9) 10.3 (248.9) 8.0 (770.8)35 Km offset 100 (4.2) 89.3 (8.8) 60.4 (21.9) 10.3 (301.1) 7.8 (693.2)40 Km offset 100 (4.2) 89.3 (8.4) 60.6 (25.0) 10.4 (316.5) 7.9 (677.8)

Table 3 provides an analysis of the yield and accuracy when the numberof satellite signals provided to a device is trimmed to the minimumcardinal number and no attempt is made to remove erroneous satellitesignals. For example, for no erroneous satellite signals, only foursatellite signals are provided to the device; for one erroneoussatellite signal, five satellite signals are provided (with oneproviding an incorrect or erroneous signal); for two erroneous satellitesignals, six satellite signals are provided (with two providingerroneous signals). Such results may be indicative of situationsoccurring in an urban environment.

TABLE 3 4 good sats 4 good sats 4 good sat 3–4 good sats 2–4 good sats 0bad sats 1 bad sat 2 bad sats 3 bad sats 4 bad sats  1 Km offset 88.0(11.8) 21.1 (18752) 9.9 (3504) 9.6 (3051) 9.5 (3140)  5 Km offset 88.0(11.8) 22.0 (18714) 9.9 (2784) 9.6 (3261) 9.6 (3140) 10 Km offset 87.9(11.8) 22.3 (18723) 9.7 (3578) 9.7 (3017) 9.6 (2854) 15 Km offset 88.0(11.8) 22.1 (18869) 9.7 (3840) 9.5 (3231) 9.5 (3102) 20 Km offset 87.9(11.8) 21.7 (19148) 10.0 (3516)  9.7 (3244) 9.5 (3097) 25 Km offset 87.9(11.8) 21.7 (18383) 9.8 (3627) 9.7 (3033) 9.4 (2800) 30 Km offset 88.0(11.8) 21.5 (18606) 10.0 (3722)  9.6 (3071) 9.4 (2944) 35 Km offset 88.0(11.9) 21.5 (18402) 9.6 (3365) 9.5 (2920) 9.5 (2903) 40 Km offset 87.8(11.9) 21.2 (18158) 9.6 (3567) 9.5 (2862) 9.6 (2899)

With reference to Table 3, it is illustrated that upon receipt of atleast one erroneous satellite signal, the yield drops off significantlyand unacceptably.

Table 4 provides an analysis of yield after pre-processing of aplurality of satellite signals by a device utilizing an exemplaryalgorithm according to the present subject matter. The resultsidentified in Table 4 may be indicative of situations encountered in aregional or country environment where there exists little signalinterference and cells are likely to be large (up to 40 km).

TABLE 4 0 bad sats 1 bad sat 2 bad sats 3 bad sats 4 bad sats  1 Kminitial offset 100 (4.2) 100 (27.8) 100 (379) 99.4 (2406) 79.6 (10455) 5 Km offset 100 (4.2) 100 (23.5) 100 (394) 99.4 (2460) 79.6 (10141) 10Km offset 100 (4.2) 100 (23.8) 100 (408) 99.3 (2490) 79.6 (10312) 15 Kmoffset 100 (4.2) 100 (27.3) 100 (379) 99.3 (2464) 79.6 (20822) 20 Kmoffset 100 (4.2) 100 (30.1) 100 (357) 99.4 (2482) 79.6 (20914) 25 Kmoffset 100 (4.2) 100 (23.8) 100 (380) 99.4 (2519) 79.6 (10270) 30 Kmoffset 100 (4.2) 100 (24.9) 100 (348) 99.4 (2409) 79.5 (10135) 35 Kmoffset 100 (4.2) 100 (21.5) 100 (360) 99.4 (2413) 79.5 (10075) 40 Kmoffset 100 (4.2) 100 (25.8) 100 (335) 99.3 (2391) 79.5 (9872) 

Table 5 shows the yield and accuracy by a device utilizing an exemplaryalgorithm according to the present subject matter when the number ofsatellite signals provided to a device is trimmed to the minimumcardinal number. For example, for no erroneous satellite signals, onlyfour satellite signals are provided to the device; for one erroneoussatellite signal, five satellite signals are provided (with oneproviding an incorrect or erroneous signal); for two erroneous satellitesignals, six satellite signals are provided (with two providingerroneous signals). Such results may be indicative of situationsoccurring in an urban environment.

TABLE 5 4 good sats 4 good sats 4 good sat 3–4 good sats 2–4 good sats 0bad sats 1 bad sat 2 bad sats 3 bad sats 4 bad sats  1 Km offset 87.9(11.7) 91.9 (1427) 94.0 (1851) 95.4 (1914) 96.0 (1944)  5 Km offset 88.0(11.6) 92.0 (1587) 94.0 (1921) 95.3 (2126) 96.0 (2255) 10 Km offset 87.8(11.6) 91.9 (1630) 94.0 (1851) 95.3 (2513) 95.9 (2756) 15 Km offset 87.7(11.7) 91.8 (1925) 94.0 (2690) 95.5 (3124) 96.0 (3533) 20 Km offset 87.9(11.7) 91.9 (2229) 94.1 (3265) 95.5 (3952) 95.9 (4509) 25 Km offset 87.9(11.7) 91.7 (2620) 93.8 (3991) 95.1 (4968) 95.9 (5793) 30 Km offset 88.0(11.9) 91.8 (3112) 93.9 (4961) 95.4 (6203) 95.8 (7305) 35 Km offset 88.0(11.9) 91.9 (3647) 93.8 (5870) 95.2 (7611) 95.7 (8987) 40 Km offset 88.1(11.9) 91.8 (4320) 93.8 (7101) 95.2 (9045)  95.8 (10650)

With reference to Tables 1-3, it has been illustrated that when nopre-processing of GPS signals occurs, the corresponding yield dropssignificantly depending upon the number of satellites providingerroneous signals. For example, with one erroneous satellite signal theyield drops to 90%, with two erroneous satellite signals the yield dropsto 60%, with three erroneous satellite signals the yield drops to 10%,and with four erroneous satellite signals the yield drops to 8%. To thecontrary, the technique according to the present subject matter producesa far superior result in terms of yield as shown in Tables 4 and 5.

FIG. 4 is a schematic representation for implementing one embodiment ofthe present subject matter. With reference to FIG. 4, a satellite system410 communicates with a ground system 420. The ground system 420 mayinclude a cellular network having a location center 421. The locationcenter 421 may be a Mobile Location Center (MLC) a central officeconfigured to communicate with a telecommunication network 422 and atleast one base station 423. In one embodiment of the present subjectmatter, a device 424 communicates with the base station 423 to acquireGPS assistance data. The location center 421 may communicate apreliminary estimate of the receiver's location on the basis of thereceiver's cell site. This information may then be relayed to the mobilereceiver and used for location determination. The location center 421may also receive satellite information from a GPS satellite. Thesatellite information may include the satellite's broadcast ephemerisinformation of the broadcasting satellite or that of all satellites. Thelocation center 421 may relay the information back to the device 424 oruse the information, either singularly or along with some preliminaryestimation of the device's location, to assist the device in ageographic location determination. In another embodiment, the stepsillustrated in FIGS. 2 and 3 may be implemented at the location center421 and communicated to the device 424.

An apparatus according to one embodiment of the present subject mattermay include a receiver or mobile device. The receiver may be utilizedfor cellular communication in any conventional communication format. Thereceiver may be, for example, a cellular device, a text messagingdevice, a computer, a portable computer, a vehicle locating device, avehicle security device, a communication device, or a wirelesstelephone. If the receiver is a cellular device, the approximatelocation of the receiver may be defined as a function of an area of acell in a cellular network, or alternatively, as a function of alocation of one or more base stations in the cellular network. Thereceiver may receive a first plurality of signals comprising one signalfrom each of a first plurality of satellites. The receiver or device mayalso contain circuitry for determining a first location of the device asa function of the first plurality of signals and circuitry fordetermining a second location of the apparatus as a function of a secondplurality of signals if the first location is not within a predeterminedthreshold, wherein the second plurality of signals is a first subset ofthe first plurality of signals. The receiver may also determine a thirdlocation as a function of a third plurality of signals if the secondlocation is not within the predetermined threshold, wherein the thirdplurality of signals is a second subset of the first plurality ofsignals. The receiver may receive signals from satellites that are apart of GNSS such as GPS, QZSS, Galileo and GLONASS. The predeterminedthreshold may be defined by ephemeris information transmitted by one ofthe satellites, the lowest sum of the squared residuals, or from otherinformation utilized in the art to determine the quality of a signal.

An apparatus according to an embodiment of the present subject mattermay also include one or more processors configured to process geographiclocation information. In one embodiment of the present subject matter,an apparatus comprises a receiver for receiving signals from each of aplurality of satellites, a processor or other circuitry for determininga first location of the device as a function of a quality of thereceived signals for determining a second location of the device as afunction of a subset of said received signals if said quality is notwithin a predetermined threshold. Such a processor(s) or circuitry maybe programmed with instructions similar to those represented in theembodiments represented in FIGS. 2 and 3. Once the erroneous satellitesignals have been identified, the one or more GPS processors may conducta geographic location estimation based on the signals obtained from theunaffected satellites. Of course, the apparatus may be a mobile unitsuch as a cellular telephone, text messaging device, computer, portablecomputer, vehicle locating device, vehicle security device,communication device, wireless transceiver, or the like. Furthermore,the apparatus may receive signals from a cellular network and conduct aposition determination as a function of information provided by thecellular network.

One method according to an embodiment of the present subject mattercomprises receiving a first plurality of signals comprising one signalfrom each of a first plurality of satellites and determining a firstlocation of the device as a function of the first plurality of signals.If the first location is not within a predetermined threshold, then themethod comprises determining a second location of the device as afunction of a second plurality of signals wherein the second pluralityof signals is a first subset of the first plurality of signals. Ofcourse, if the second location is not within a predetermined threshold,then the method may further comprise determining a third location of thedevice as a function of a third plurality of signals wherein the thirdplurality of signals is a second subset of the first plurality ofsignals.

Another method according to one embodiment of the present subject matterincludes receiving a plurality of signals from a plurality ofsatellites, generating estimates of a location of the device usingcombinations of the plurality of signals, and selecting an estimate asdefined by a quality of each of the combinations. The satellites may bea part of a GNSS such as GPS, Galileo, GLONASS, or QZSS. The quality maybe defined by a sum of the squared residuals, ephemeris information orother information in the art adaptable to define a quality of such asignal. The device may be a mobile unit such as a cellular telephone,text messaging device, computer, portable computer, vehicle locatingdevice, vehicle security device, communication device, and wirelesstransceiver. Of course, if the device is a mobile unit, the device mayreceive signals form a cellular network to thereby assist in thelocation thereof.

One method according to an embodiment of the present subject mattercomprises the steps of receiving a first plurality of observations froma first plurality of satellites and determining a first position of thedevice as defined by a quality of the first plurality of observations.If the quality of the first plurality of observations fails to meet thepredefined threshold then the device or associated processor maydetermine a second position of the device as defined by a quality of asecond plurality of observations, the second plurality being a subset ofthe first plurality of observations. If the quality of the secondplurality of observations fails to meet the predefined threshold thenthe device may calculate additional positions utilizing incrementallydecreasing subsets of observations until a predetermined criteria isachieved. Exemplary criteria may be where a cardinality of observationsis at least four, where the quality meets the predefined threshold, orwhere the quality of all subsets or combinations of satelliteobservations have failed to meet the predefined threshold. Of course,the quality may be defined by a sum of the squared residuals, ephemerisinformation or other information in the art adaptable to define aquality of such a signal. If the device is receiving signals from acellular network, the quality may also be defined by informationprovided from the cellular network.

It is as aspect of the present subject matter to provide an ability tocalculate a device or handset location in the presence of erroneoussatellite signals to ensure that there is no performance impact forassociated location services.

It is also an aspect of the present subject matter to significantlyimprove yield when there is a small number of measured satellite signalsand one signal is erroneous. Embodiments of the present subject mattermay result in a substantially one hundred percent yield even when thereare several satellites having erroneous signals, and embodiments of thepresent subject matter operate well under incorrect cell provisioning.

As shown by the various configurations and embodiments illustrated inFIGS. 1-4, a method and apparatus for determining the geographiclocation of a device have been described.

While preferred embodiments of the present subject matter have beendescribed, it is to be understood that the embodiments described areillustrative only and that the scope of the invention is to be definedsolely by the appended claims when accorded a full range of equivalence,many variations and modifications naturally occurring to those of skillin the art from a perusal hereof.

1. A method for determining the location of a device comprising thesteps of: (a) receiving a first plurality of signals comprising onesignal from each of a first plurality of satellites; (b) determining afirst location of the device as a function of the first plurality ofsignals; and (c) determining a second location of the device as afunction of a second plurality of signals if the first location is notwithin a predetermined threshold, wherein the second plurality ofsignals is a first subset of the first plurality of signals.
 2. Themethod of claim 1 wherein a cardinality of the second plurality ofsignals is at least four.
 3. The method of claim 1 further comprisingthe step of: (d) determining a third location of the device as afunction of a third plurality of signals if the second location is notwithin the predetermined threshold, wherein the third plurality ofsignals is a second subset of the first plurality of signals.
 4. Themethod of claim 3 wherein a cardinality of the second plurality ofsignals is the same as a cardinality of the third plurality of signals.5. The method of claim 3 wherein a cardinality of the second pluralityof signals is greater than a cardinality of the third plurality ofsignals.
 6. In a method for eliminating erroneous satellite signals in aposition calculation for a device receiving a first plurality of signalsfrom a first plurality of satellites, the improvement comprising thesteps of determining a first position calculation of the device as afunction of the first plurality of signals and determining a secondposition calculation of the device as a function of a second pluralityof signals if the first calculation is not within a predeterminedthreshold, wherein the second plurality of signals is a first subset ofthe first plurality of signals.
 7. The method of claim 6 wherein thedevice is receiving signals from a cellular network.
 8. The method ofclaim 7 wherein a position calculation of the device is a function ofsignals provided by the cellular network.
 9. The method of claim 6wherein the satellites are part of a Global Navigation Satellite System(“GNSS”).
 10. The method of claim 9 wherein the GNSS is selected fromthe group consisting of: Global Positioning System (“GPS”), Galileo,GLONASS, and Quasi-Zenith Satellite System (“QZSS”).
 11. The method ofclaim 6 wherein the device is a mobile unit.
 12. The method of claim 11wherein the mobile unit is selected from the group consisting of:cellular device, text messaging device, computer, portable computer,vehicle locating device, vehicle security device, communication device,and wireless transceiver.
 13. The method of claim 6 wherein acardinality of the second plurality of signals is at least four.
 14. Themethod of claim 6 further comprising the step of determining a thirdlocation of the device as a function of a third plurality of signals ifthe second location is not within the predetermined threshold, whereinthe third plurality of signals is a second subset of the first pluralityof signals.
 15. The method of claim 14 wherein a cardinality of thesecond plurality of signals is the same as a cardinality of the thirdplurality of signals.
 16. The method of claim 14 wherein a cardinalityof the second plurality of signals is greater than a cardinality of thethird plurality of signals.
 17. In a method for determining the locationof a device receiving signals from each of a plurality of satellites,the device having determined a first location from the received signals,the improvement comprising the steps of: (a) comparing a quality of thefirst location of the device with a predetermined threshold; and (b)determining a second location of the device from a first subset of thereceived signals if the quality of the first location is not within thepredetermined threshold.
 18. The method of claim 17 wherein the qualityis defined by a lowest sum of the squared residuals.
 19. The method ofclaim 17 wherein at least one of the received signals is provided by acellular network.
 20. The method of claim 19 wherein the quality is afunction of information provided by the cellular network.
 21. The methodof claim 17 wherein the satellites are part of a Global NavigationSatellite System (“GNSS”).
 22. The method of claim 21 wherein the GNSSis selected from the group consisting of: Global Positioning System(“GPS”), Galileo, GLONASS, and Quasi-Zenith Satellite System (“QZSS”).23. The method of claim 17 wherein the device is a mobile unit.
 24. Themethod of claim 23 wherein the mobile unit is selected from the groupconsisting of: cellular device, text messaging device, computer,portable computer, vehicle locating device, vehicle security device,communication device, and wireless transceiver.
 25. The method of claim17 further comprising the step of determining a third location of thedevice as a function of a second subset of the received signals if thequality of the second location is not within the predeterminedthreshold.
 26. The method of claim 25 wherein a cardinality of thesignals defining the first subset is at least four.
 27. The method ofclaim 25 wherein a cardinality of the signals defining the first subsetis greater than the cardinality of the signals defining the secondsubset.
 28. A method for determining the location of a device comprisingthe steps of: (a) receiving a plurality of signals from a plurality ofsatellites; (b) generating estimates of a location of the device usingcombinations of the plurality of signals; and (c) selecting an estimateas defined by a quality of each of the combinations.
 29. The method ofclaim 28 wherein a cardinality of the plurality of signals is at leastfour.
 30. The method of claim 28 wherein the satellites are part of aGlobal Navigation Satellite System (“GNSS”).
 31. The method of claim 30wherein the GNSS is selected from the group consisting of: GlobalPositioning System (“GPS”), Galileo, GLONASS, and Quasi-Zenith SatelliteSystem (“QZSS”).
 32. The method of claim 28 wherein the quality is afunction of a sum of the squared residuals.
 33. The method of claim 28wherein the device is a mobile unit.
 34. The method of claim 33 whereinthe mobile unit is selected from the group consisting of: cellulartelephone, text messaging device, computer, portable computer, vehiclelocating device, vehicle security device, communication device, andwireless transceiver.
 35. The method of claim 33 wherein the mobile unitreceives signals from a cellular network.
 36. The method of claim 35wherein the estimate of a location of the device is a function ofsignals provided by the cellular network.
 37. A device comprising: areceiver for receiving a first plurality of signals comprising onesignal from each of a first plurality of satellites; a means fordetermining a first location of the device as a function of the firstplurality of signals; and a means for determining a second location ofthe device as a function of a second plurality of signals if the firstlocation is not within a predetermined threshold, wherein the secondplurality of signals is a first subset of the first plurality ofsignals.
 38. The device of claim 37 further comprising a means fordetermining a third location of the device as a function of a thirdplurality of signals if the second location is not within thepredetermined threshold, wherein the third plurality of signals is asecond subset of the first plurality of signals.
 39. The device of claim37 wherein the satellites are part of a Global Navigation SatelliteSystem (“GNSS”).
 40. The device of claim 39 wherein the GNSS is selectedfrom the group consisting of: Galileo, GLONASS, and Quasi-ZenithSatellite System (“QZSS”).
 41. The device of claim 37 wherein thesatellites are Global Positioning System (“GPS”) satellites.
 42. Thedevice of claim 37 wherein the predetermined threshold is a function ofephemeris information transmitted by one of the satellites.
 43. Thedevice of claim 37 wherein the predetermined threshold is a function ofa lowest sum of the squared residuals.
 44. The device of claim 37wherein the device is a mobile unit.
 45. The device of claim 44 whereinthe mobile unit is selected from the group consisting of: cellulardevice, text messaging device, computer, portable computer, vehiclelocating device, vehicle security device, communication device, andwireless transceiver.
 46. The device of claim 45 wherein the mobile unitis adaptable to receive signals from a cellular network.
 47. The deviceof claim 46 wherein the predetermined threshold is a function ofinformation received from the cellular network.
 48. A system fordetermining a location of a device from signals received from aplurality of Global Navigation Satellite System (“GNSS”) satellitescomprising: a receiver for receiving signals from each of a plurality ofsatellites; a means for determining a first location of the device as afunction of a quality of the received signals; and a means fordetermining a second location of the device as a function of a subset ofsaid received signals if said quality is not within a predeterminedthreshold.
 49. The system of claim 48 wherein the satellites are part ofa Global Navigation Satellite System (“GNSS”).
 50. The system of claim49 wherein the GNSS is selected from the group consisting of: Galileo,GLONASS, and Quasi-Zenith Satellite System (“QZSS”).
 51. The system ofclaim 48 wherein the satellites are Global Positioning System (“GPS”)satellites.
 52. The system of claim 48 wherein said quality is afunction of ephemeris information transmitted by at least one satellite.53. The system of claim 48 wherein said quality is a function of alowest sum of the squared residuals determined from said signals. 54.The system of claim 48 wherein the device is a mobile unit.
 55. Thesystem of claim 54 wherein the mobile unit is selected from the groupconsisting of: cellular device, text messaging device, computer,portable computer, vehicle locating device, vehicle security device,communication device, and wireless transceiver.
 56. The system of claim54 wherein the mobile unit receives signals from a cellular network. 57.The system of claim 56 wherein the location of the device is a functionof information provided by the cellular network.
 58. A method ofcalculating the position of a device comprising the steps of: (a)receiving a first plurality of observations from a first plurality ofsatellites; (b) determining a first position of the device as a functionof a quality of the first plurality of observations; (c) if the qualityof the first plurality of observations fails to meet the predefinedthreshold then: (i) determining a second position of the device asdefined by a quality of a second plurality of observations, the secondplurality being a subset of the first plurality of observations, (ii) ifthe quality of the second plurality of observations fails to meet thepredefined threshold then repeating step (i) using incrementallydecreasing subsets of observations until a predetermined criteria isachieved.
 59. The method of claim 58 wherein the criteria is acardinality of observations is at least four.
 60. The method of claim 58wherein the criteria is the quality meets the predefined threshold. 61.The method of claim 58 wherein the criteria is the quality of allcombinations of satellite observations have failed to meet thepredefined threshold.
 62. The method of claim 58 wherein the quality isa function of a lowest sum of the squared residuals.
 63. The method ofclaim 58 wherein the device is receiving signals from a cellularnetwork.
 64. The method of claim 63 wherein the quality is a function ofinformation provided from the cellular network.
 65. The method of claim58 wherein the satellites are part of a Global Navigation SatelliteSystem (“GNSS”).
 66. The method of claim 65 wherein the GNSS is selectedfrom the group consisting of: Global Positioning System (“GPS”),Galileo, GLONASS, and Quasi-Zenith Satellite System (“QZSS”).
 67. Themethod of claim 58 wherein the device is a mobile unit.
 68. The methodof claim 67 wherein the mobile unit is selected from the groupconsisting of: cellular device, text messaging device, computer,portable computer, vehicle locating device, vehicle security device,communication device, and wireless transceiver.